Coiled tubing is commonly used in the oilfield industry, and it is also becoming more common to employ continuous coiled rod instead of conventional sucker rod, for example for the purpose of driving downhole pump equipment, thereby avoiding the need to thread together discrete rod sections via threaded couplers at the ends thereof.
Injectors for coiled tubing or continuous rod typically employ a pair of endless chains driven in counter-rotating directions in a common upright plane, and carrying gripper dies or blocks on the chains that have outward facing gripping surfaces to clench the continuous rod between the faces of opposed gripper dies on the two chains as they descend downward on adjacent, facing-together, parallel sides of the two chain paths. A respective skate is found inside the area around which each chain is driven in order to lie along this descending side of the chain, and the skates are displaceable toward one another by hydraulic cylinders, thereby forcing the descending gripper blocks toward one another to firmly grip the coil tubing or continuous rod between them.
Prior art in the general area of injector heads and gripper dies for same includes U.S. Pat. Nos. 5,094,340, 5,553,668, 5,918,671, 6,425,441, U.S. Pat. Nos. 6,516,891, 6,609,566, 6,880,629, 6,892,810, 7,051,814, 7,857,042 and 8,132,617, and U.S. Patent Application Publication 2012/0222855.
Skates for injector heads have typically employed cylindrical rollers to apply force against the bases of the gripper dies, either by rotatably supporting rollers at fixed locations along the side of the skate body or by using roller chain that is entrained around the skate body.
However, Applicant has developed a unique skate design employing spherical balls instead of cylindrical rollers as the roller elements over which the gripper dies move as they are forced together by the skates.